Foldable head rest assemblies have been known in the prior art for quite some time. U.S. Pat. No. 7,325,877 B2 discloses a foldable head rest assembly for a vehicle that comprises a bracket and an armature attached to the bracket. The armature is pivotable about a first axis and connected to the bracket by means of an armature shaft. The armature shaft is not formed from a single piece but split up into two separate pieces, each piece connecting one of the two arms of the armature to the bracket. The head rest assembly further comprises a locking mechanism that can engage with one arm of the armature to lock the armature in an upright or in-use position. To be able to pivot or orbit the armature into a folded position a release mechanism is provided that can move the locking mechanism from a locked position to an unlocked position. In the upright position an abutment surface of the arms of the armature engages with the bracket to prevent further pivoting or tilting away from the folded position, wherein the locking mechanism prevents any pivoting towards the folded position.
For a secure locking of the armature in the upright position the armature shaft needs to be precisely arranged between the locking shaft and the bracket. Any deviation from the design distances of the shafts and the bracket may lead to a failure of the locking mechanism. Hence, a secure locking depends at least on the position of the armature shaft with respect to the bracket and the locking shaft and, in particular, the engaging surfaces provided on the bracket, the arms and the locking mechanism. Said arrangement is, however, prone to deviations due to tolerances in the production of the elements of the head rest assembly. With an increasing number of parts that have to be exactly aligned with respect to one another the risk of a failure of the locking mechanism increases.
U.S. Pat. No. 8,002,256 B2 also discloses a foldable head rest assembly for a vehicle comprising a bracket and an armature mounted to said bracket. The armature carries a head rest and is movable between a folded position and an upright or in-use position. The armature is pivoted with respect to the bracket about a first axis. The head rest assembly further comprises a locking mechanism having a locked and an unlocked position. The locking mechanism engages with a locking element that is attached to an armature shaft to which the first arm and the second arm of the armature are connected. The locking mechanism does not directly engage with any of the arms of the armature. Instead the locking element and the armature are rotatably connected by means of the armature shaft. To move the locking mechanism from the locked to the unlocked position a release mechanism is provided that is pivotable about the first axis.
Another head rest assembly is known from U.S. 2008/0036263 A1. The foldable head rest assembly disclosed therein also comprises a bracket and an armature for carrying a head rest. The armature is pivotable with respect to the bracket about a first axis between an upright position and a folded position. In the upright position an abutment surface of each arm of the armature engages with the bracket to prevent further movement or pivoting of the armature away from the folded position. Pivoting of the armature towards the folded position can be restricted by a locking mechanism. The locking mechanism is pivotable about a second axis that extends in parallel to the first axis and is spaced apart from the first axis. The locking mechanism engages with the first arm of the armature and prevents any movement of the armature towards the folded position. To move the locking mechanism from the locked position to the unlocked position a release mechanism that is pivotable about a second axis has to be turned.